Pernicious Anemia Mimicking Thrombotic Thrombocytopenic Purpura in the Setting of Severe Vitamin B12 Deficiency.

Pernicious anemia (PA) is an autoimmune-mediated vitamin B12 deficiency that classically presents with macrocytic anemia and neurologic dysfunction. The case described highlights a rare variant of PA that paralleled concerns for microangiopathic hemolytic anemia (MAHA) like thrombotic thrombocytopenic purpura (TTP). A 40-year-old African American female with limited past medical history presented with progressive fatigue, lower-extremity weakness, gait instability, and ataxia, accompanied by chronic gastrointestinal symptoms, weight loss, and menorrhagia. Initial evaluation revealed profound macrocytosis, pancytopenia, laboratory evidence of hemolysis, including an elevated lactate dehydrogenase (LDH) and undetectable haptoglobin level without evidence of acute kidney injury (AKI), and neurologic deficits concerning for subacute combined degeneration. This case was complicated by right lower lobe pneumonia, urinary tract infection, and a left Bartholin cyst. Further testing demonstrated elevated methylmalonic acid and homocysteine levels, positive intrinsic factor (IF) antibodies, and only mildly reduced ADAMTS13 activity, which confirmed the diagnosis of PA. The patient was treated with parenteral vitamin B12, folate, and supportive care, resulting in gradual recovery. Although inpatient rehabilitation was recommended, the patient declined and was instead discharged home with arrangements for outpatient follow-up and lifelong intramuscular vitamin B12 replacement therapy. This case underscores the importance of recognizing that, in rare cases, PA can present as a mimicker of thrombotic microangiopathies such as TTP, as early identification can prevent unnecessary therapeutic intervention, reduce morbidity, and facilitate timely, disease-specific therapy.